This invention relates to CAD/CAM systems and automatic programming units, and more particularly to a curve-surface forming system of forming curved surfaces by using curves.
One example of the conventional technology of this type is the curve-surface defining and forming system disclosed by the publication "Kikai Gijutsu (Mechanical Technology) Vol. 35, No. 13" p 105-106, which is as shown in FIG. 1.
In FIG. 1, reference numeral 1 designates a curve inputting means for inputting curves forming a curved surface; 6, a curve consulting means for referring to a curve to obtain data on the curve in a parametric mode; and 5, a curved surface forming means for forming a curve surface by using the data on the curve thus obtained. This system is practiced by an electrical circuit as shown in FIG. 2. In FIG. 2, reference numeral 17 designates an inputting unit comprising a key board, mouse, function keys, etc.; 18, a CPU; 19, a memory unit including memories, magnetic discs, etc.; and 20, an outputting unit including a CRT, puncher, printer, plotter, etc.
The operation of the system will be described. As a premise for description, the term "curve definition direction" as used herein is intended to mean the direction in which, in referring to a curve in a parametric mode, the curve advances spatially with increasing parameters. In the figures referred to below, the curve definition direction is indicated by the arrow. And it is assumed that in a coordinate system on a curved surface, i.e., in a spherical coordinate system, the positions of points on the curve surface are determined by two curved-surface parameters U and V.
A curved-surface forming procedure shown in FIG. 3 will be described with reference to FIG. 4. In FIG. 4, reference characters A.sub.1, A.sub.2, B.sub.1 and B.sub.2 designate parametric curves. First, the curves are inputted using the curve inputting means, and each curve is consulted in the curve definition direction by the curve consulting means 6, so that a curved surface is formed by the curve surface forming means 5 using the curve line data obtained through the consultation.
As is apparent from the above description, in the conventional method, the curves forming the curved surface must be defined in the same direction as the curved-surface parameters U and V as shown in FIG. 4. Therefore, in defining a curved surface, the curves must be inputted in accordance with the rule of curve definition direction which intuitively is difficult to understand. If an error is made with the curve definition direction, then the aimed curved surface will not be formed at all.